1. Field of the Invention
The present invention relates to a system for controlling the voltage furnished to an electrically assisted power steering system in an automotive vehicle.
2. Disclosure Information
Automotive designers typically determine the size of electrically assisted power steering motors based on the maximum torque requirement and a given level of voltage (typically 13.5 volts in a 12 volt system). Such motors must be sized to provide sufficiently high torque at low speeds for parking conditions, as well as sufficient torque at higher speeds for sudden evasive maneuvers. Of course, optimal response time comes at the expense of increased motor size and weight.
The present inventors have determined that by increasing the voltage available to the motor on demand, thereby increasing the torque output of the motor, a smaller and lighter electric motor may be used in an electric power steering system, simply because greater torque is available without a larger motor.
U.S. Pat. No. 5,668,721 illustrates a system in which an electric power steering motor is controlled in two modes of operation, a voltage mode and a current mode, with each mode producing different operational characteristics. The system of the '721 patent and other known systems powering the steering motor utilize only the voltage level being maintained by the vehicle's electrical system to drive the motor. In contrast, a system according to the present invention increases the voltage available to a steering motor in high-assist situations by shedding electric loads imposed by power consuming components and, where appropriate, by increasing power output from the power source whenever high-assist steering situations are present.